1. Field of the Invention
The present invention relates to a structure of a resin-molded or resin-sealed optical semiconductor integrated circuit device including a lead frame and a transparent resin, in particular, to a structure of an optical semiconductor integrated circuit device having excellent thermal discoloration resistance and crack resistance against high-temperature reflow in the implementation of mounting the optical semiconductor integrated circuit device to equipment.
2. Description of the Related Art
A transparent epoxy resin composition is generally used for resin-molding or resin-sealing an optical semiconductor element such as a light-sensitive element and a light-emitting element mounted in a compact disk (CD) player, a digital versatile disk (DVD) player, or the like.
Electronic appliances have become smaller and lighter while attaining more advanced performance in recent years. This also promoted higher density mounting and surface mounting of optical semiconductor packages.
Examples of such surface-mounting packages include two-way flat packages (small outline packages (SOPs)), four-way flat packages (quad flat packages (QFPs)), and small outline non-lead (SON) packages.
Recently, a package including a lead frame having a silver-plated surface is increasingly used as this type of package.
However, in order to mount such an optical semiconductor device in the form of a surface-mounting package, a solder reflow process is necessary. Moreover, in recent years, regulation on lead has become more stringent due to environmental reasons, and this rendered it necessary to use high temperature as the reflow temperature. As a consequence, heat resistance up to 260° C. has become necessary. Furthermore, when a known epoxy resin composition is used in the reflow step, the package itself absorbs moisture before being exposed to a high temperature. Therefore, the absorbed moisture vaporizes to form moisture vapor during the solder reflow, and the moisture vapor pressure disadvantageously causes the optical semiconductor element to delaminate from the molding resin (cured member).
A typical approach for resolving this problem of delamination of the molding resin by the moisture vapor is to incorporate a large amount of a high-strength structural material such as filler in the molding resin, to increase adhesion between the resin and the substrate and between the resin and the semiconductor, or the like. However, in an optical semiconductor device that emits/receives light, a filler or the like cannot be mixed in the resin because of its special characteristics. Moreover, there is a limit to increasing the adhesion because the color of resin should be prevented from changing. In particular, unlike in other individual optical semiconductors such as LEDs, in an optical integrated circuit including enlarged optical semiconductor elements, it has become difficult to solve the problem due to the increased size of the optical semiconductor device itself.
Under these circumstances, one example of a highly heat-resistant and highly moisture-resistant device structure for an optical semiconductor that can be listed here is an example of an optical integrated circuit including a resin substrate (refer to Japanese Unexamined Patent Application Publication No. 2003-46034 (pp. 3-4, in the Japanese specification and FIGS. 1 and 3)). This optical integrated circuit has a structure in which some metal wires on the resin substrate are made to extend outside a molding resin so that the moisture inside the optical semiconductor device can be drained by utilizing the inherent characteristics of transparent resin having a low adhesiveness on a metal. However, this structure cannot completely resolve the problems of the optical integrated circuit device including a lead frame, namely, the problems of delamination during high-temperature solder reflow (260° C.) and discoloration in the molding resin.
Moreover, as an example of a highly heat-resistant and highly moisture-resistant molding resin for optical semiconductor including a lead frame, there is an example of altering and improving the material contained in the molding resin (refer to Japanese Unexamined Patent Application Publication No. 2003-268200 (pp. 2 to 7 in the Japanese specification)), which is a transparent epoxy resin composition containing a thiol-based compound and a coupling agent so that the adhesion between the resin and the lead frame can be decreased and the moisture inside the optical semiconductor device can be discharged from the interface between the lead frame and the molding resin. However, when an optical semiconductor device including a lead frame is subjected to a high-temperature solder reflow (260° C.) by using this transparent epoxy resin composition, delamination, resin clacking, and discoloration of resin still occur. Thus, it has not been possible to solve the problems.